[Haskell-cafe] Non-traversable foldables

Henning Thielemann lemming at henning-thielemann.de
Fri Oct 9 10:45:01 EDT 2009

On Fri, 9 Oct 2009, Martijn van Steenbergen wrote:

> Hallo café,
> Can anyone think of datatypes that are Foldable but not Traversable?
> If not, what is the purpose of having a separate Foldable class?

Recently I wondered, why Foldable is superclass of Traversable, since I 
have examples where 'traverse' makes sense, but 'fold' not.


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